The present invention relates to a reciprocating device for a movable member, such as a movable cover of household electrical appliances.
A known reciprocating device of this type comprises, for example, a stationary member, a movable member held by this stationary member in such a manner as to be reciprocated, biasing means provided between the movable member and the stationary member and adapted to bias the movable member in at least one of the reciprocating directions, and a lock device for stopping the movable member in the course of its reciprocation (see, for example, Japanese Patent Laid-Open No. 64-41434).
The above-mentioned lock device is equipped with a cam groove provided on either the stationary or the movable member and extending around a heart-shaped island, a lock pin whose base end section is rotatably supported by either the stationary or the movable member and whose tip end section is bent toward the bottom of the above-mentioned cam groove, and pressing means for pressing the tip end section of this lock pin toward the bottom of the cam groove.
The above cam groove is equipped with an introduction path extending toward a point tapered section of the heart-shaped island, a former path extending from this introduction path along one side of the heart-shaped island while gradually decreasing its depth, a turn-back section which is one step deeper than the shallowest end of the forward path and equipped with a dead end, a stop section which is adjacent to and still one step deeper than the turn-back section and which extends along the pit section of the heart-shaped island in the middle of the other end portion thereof, an escape section which is adjacent to and one step deeper than the stop section and which extends toward the other side of the heart-shaped island up to a dead end, and a return path which extends along the other side of the heart-shaped island while decreasing its depth to communicate with the above introduction path and whose shallowest end is one step higher than the bottom of the introduction path.
Further, the present applicant has already proposed a structure having a groove-like by-pass extending across the central portion of the heart-shaped island, from the stop section toward the introduction path thereof (see Japanese Patent Application No. 2-176941).
The end section facing the stop section of the by-pass is formed one step shallower than the bottom of the stop section, and a tapered surface is formed thereon which is inclined toward the bottom of the stop section of the cam groove. The tip end section of the lock pin is bent obliquely toward the bottom of the stop section of the cam groove.
A problem with the above-described conventional reciprocating device is that the movable member thereof is liable to break if it is forcibly moved in the lock-releasing direction when in a locked position.
The locked state of the lock device can be released by moving the movable member in the locking direction again. When the movable member is moved in that direction, the tip end section of the lock pin advances from the stop section to the escape section of the cam groove, thereby releasing the lock.
If, in contrast, the movable member is forcibly moved in the lock-releasing direction, the tip end section of the lock pin, which is in the stop section of the cam groove, abuts the pit section of the heart-shaped island, and prevents any further movement of the movable member.
However, in the case of household electrical appliances, a person, such as a child, who is not accustomed to use the apparatus, may attempt to forcibly move the movable member. Such a person may try to forcibly open the movable cover of the apparatus which has been locked by means of the reciprocating device.
In such a case, the pit section of the heart-shaped island of the cam groove may be scraped or broken off by the tip end section of the lock pin. Or, conversely, the tip end section of the lock pin may be bent or broken as a result of being pressed by the pit section of the heart-shaped island.